- using psm0 instead of sysmouse is a workaround
- using xf86-input-mouse-1.2.1 will reportedly prevent the problem

According to Joerg, the issue is actually that the signal handlers
(presumably in xf86-input-mouse) use floating point state, which is
currently not saved/restored in the dragonfly signal handling code.

Not sure why as discussed in this bug, GTK appears to trigger
the problem, but my guess is that is a red herring, although hacking
the specific pkg makefile / patches might result in a good debug binary.